This application claims the priority of German Application No. 199 20 181.1 filed May 3, 1999, which is incorporated herein by reference.
Electromagnetic actuators are essentially composed of at least one electromagnet and an armature which is coupled with a component to be driven by the actuator. The armature is movable, against the force of a resetting spring, by an electromagnetic field generated by the electromagnet when it is supplied with current. Such electromagnetic actuators are characterized by high armature speeds (switching speeds).
Electromagnets of the above type involve the problem that when the armature approaches the pole face of the attracting electromagnet and thus the distance between armature and pole face decreases, that is, the air gap between the pole face and the armature diminishes, the magnetic force affecting the armature exponentially increases, while, as a rule, the counter force of the resetting spring increases only linearly. As a result, the armature impacts on the pole face with increasing speed. Apart from noise generation, rebound phenomena may occur, that is, the armature first impacts on the pole face then lifts off at least for a short period until it assumes its position of rest in contact with the pole face. This occurrence may adversely affect the functioning of the driven component which, in turn, may lead to malfunctions or significant disturbances in actuators operating with high switching frequencies.
It is therefore desirable to ensure that the impact velocity of the armature is in the order of magnitude below 0.05 m/s. It is of importance that such low impact speeds are ensured under real operational conditions as well, together with all the stochastic oscillations involved therewith. External interferences such as shocks, jars or the like may, in the final approach of the armature or even after its engagement on the pole face lead to a sudden drop of the armature from the pole face.
It is an object of the invention to provide an improved regulating process which, in electromagnetic actuators of the above-outlined type, makes possible to so control the motion of the armature by controlling the current supply to the electromagnet that the armature arrives at its seat on the pole face with a low impact velocity. A sufficient holding force after arrival of the armature on the pole face has to be ensured by the engine control unit by providing a suitably regulated holding current.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the method of controlling a supply current applied to an electromagnet of an electromagnetic actuator by a control unit for obtaining a low impact speed of a reciprocating armature of the actuator upon arrival of the armature at a pole face of the electromagnet, includes the following steps: during travel of the armature toward the pole face detecting displacements of the armature and a sequence of the armature speed as actual values; comparing the actual values with a performance characteristic field stored in the control unit and relating to a predetermined relationship between armature speed and armature displacement for the armature travel toward the pole face; determining a desired value for the supply current from the comparison step; comparing an actual value for the supply current with the determined desired value; adjusting the supply current based on a difference between the actual and desired values; and applying the adjusted supply current to the electromagnet.
The above-outlined process takes advantage of up-to-date, high-speed electronic computer components. It is thus feasible to determine the momentary position and/or the velocity of the armature not only during the switching process, but it is also possible to detect the motion behavior of a plurality of actuators and to process the required motion magnitudes. Further, in case of deviations from desired values, it is feasible, by means of a suitable regulating step, to ensure for each individual actuator an optimal course for each switching cycle.
The method according to the invention advantageously utilizes the fact that a performance characteristic field inputted into the engine control unit determines the required relationship between the armature speed and the armature displacement for producing desired values of the current supply. Further, by determining the actual values of the armature motion as related to the armature displacement and armature speed, interfering factors may be controlled by changing, based on performance characteristics, the desired values for the current regulator and thus the actual value for the current of the xe2x80x9ccapturingxe2x80x9d electromagnet and thus the magnetic energy feed. This control is performed in a such a manner that the armature arrives at the pole face with an impacting speed which is only slightly above an ideal xe2x80x9czeroxe2x80x9d impact speed. xe2x80x9cPerformance characteristicsxe2x80x9d (xe2x80x9ccharacteristic fieldxe2x80x9d) within the meaning of the invention encompasses a single set of performance characteristics as well as a system of such sets which apply to a number of operating conditions.